1. Field of the Invention
The present invention relates generally to improvements in the field of fiber optics, and particularly to advantageous aspects of systems and methods for monitoring a pre-splice heat treatment of optical fibers.
2. Description of Prior Art
There is a continuing effort in the optical fiber industry to find ways to reduce optical signal loss when a first type of optical fiber is spliced to a second type of optical fiber. Splice loss may arise for a number of different reasons. For example, splice loss results when the modefield diameter of the first fiber has a modefield diameter that differs from the modefield diameter of the second fiber.
One approach that has been developed to reduce splice loss resulting from modefield diameter mismatch is to apply heat to the splice end of the fiber having the narrower modefield diameter. The applied heat causes a diffusion of the dopants in the narrower modefield fiber, causing an expansion of the modefield diameter at the splice end. Post-splice thermal treatments are described, for example, in Krause, John T. et al., xe2x80x9cSplice Loss of Single-Mode Fiber as Related to Fusion Time, Temperature, and Index Profile Alteration,xe2x80x9d Journal of Lightwave Technology, vol. LT-4, No. 7, 1986, pp. 837-40; Tam, H. Y., xe2x80x9cSimple Fusion Splicing Technique for Reducing Splicing Loss between Standard Singlemode Fibres and Erbium-Doped Fibre,xe2x80x9d Electronics Letters, vol. 27, No. 17, 1991, pp. 1597-99; and Ando, Yasuhiro, xe2x80x9cLow-Loss Optical Connector between Dissimilar Single-Mode Fibers Using Local Core Expansion Technique by Thermal Diffusion,xe2x80x9d IEEE Photonics Technology Letters, vol. 4, No. 8, 1992, pp. 1028-31.
A thermal treatment may also be applied prior to splicing. In that case, heat is applied to a lead end of a fiber having a narrower modefield. The heat causes an expansion of the fiber modefield at the lead end, thereby causing a reduction in splice loss when the fiber is spliced to a second fiber having a larger modefield diameter. However, it has proven difficult to achieve consistent results using a pre-splice heat treatment technique. In one approach, for example, empirical techniques are used to determine an optimal amount of time for heat treatment. However, because of differences in individual fibers and in operator technique, using the same amount of time for each heat treatment may not produce results with a desired level of consistency.
Aspects of the invention provide systems and methods for monitoring a pre-splice heat treatment of an optical fiber. In one described method, a lead end of a first fiber is prepared for splicing. The lead of the fiber is then loaded into a heat treatment station. While heating the lead fiber end, an optical time domain reflectometer is used to measure reflected backscatter loss from the lead fiber end. The lead fiber end continues to be heated until the measured reflected backscatter loss from the lead fiber end reaches a predetermined level. At that point, the heat treatment is discontinued.
Additional features and advantages of the present invention will become apparent by reference to the following detailed description and accompanying drawings.